The present invention relates generally to current sensing devices for electrical systems, and more particularly to automatically resettable alternating current fault indicators.
Various types of fault indicators have been constructed for detecting electrical faults in power distribution systems, including clamp-on type fault indicators, which clamp directly over cables in the systems, and test point type fault indicators, which are mounted over test points in cables or associated connectors of the system. Such fault indicators may be either of the manually reset type, wherein it is necessary that the indicators be physically reset, or of the self-resetting type, wherein the indicators are reset upon restoration of line current. Examples of such fault indicators are found in products manufactured by E. 0. Schweitzer Manufacturing Company of Mundelein, Ill., in U.S. Pat. Nos. 3,676,740; 3,816,816; 3,906,477; 4,034,360; 4,063,171; 4,068,529 and 4,234,847 of the present inventor, and in the copending applications of the present inventor; Fault Indicator Having a Remote Test Point at Which Fault Current is Indicated by Change in Magnetic Field, U.S. Pat. Ser. No. 103,042, filed Dec. 13, 1979, now abandoned, and Fault Indicator with Bidirectional Indicator Winding, U.S. Pat. Ser. No. 290,012, filed Dec. 13, 1979, now U.S. Pat. No. 4,438,403.
Detection of fault currents in self-resetting fault indicators may be accomplished by means of magnetic switch means, such as a magnetic reed switch positioned in close proximity to the conductor being monitored. Upon occurrence of an abnormally high fault-associated magnetic field around the conductor, the reed switch actuates a trip circuit which produces current flow in a trip winding to position an appropriate indicator member, such as a rotatably mounted indicator flag visible from the exterior of the indicator, to a trip or fault-indicating position. Upon restoration of current in the conductor, a reset circuit is actuated to produce current flow in a reset winding to reposition the indicator flag to a reset or non-fault indicating position. The invention described in the aforementioned U.S. patent application Ser. No. 290,012 provides an improvement in such fault indicators, in that it provides a simplified circuit for use in conjunction with a single bidirectional magnetic winding in place of separate trip and reset windings.
To minimize the power required by the trip and reset circuits in repositioning the indicator between reset and trip positions it is desirable that the indicator flag have minimal mass and minimal travel between positions. To these ends a rotatably mounted segmental-type indicator flag consisting of two indicating segments arranged on opposite sides of the axis of rotation of the flag has been utilized. The trip and reset circuits of the fault indicator are only required to rotate this flag 90.degree., in contrast to the trip and reset circuits of a conventional disc-type indicator which must rotate the indicator disc through 180.degree..
One drawback of previous 90.degree. segmental-type indicator flag assemblies has been the relatively greater space requirements and complexity of such assemblies compared to 180.degree. disc-type assemblies. This has made it difficult and unnecessarily costly to incorporate these segmental-type assemblies in the smaller indicator housings preferred in many monitoring applications. The present invention is directed to a new and improved actuator assembly which allows 90.degree. segmental-type indicator flag systems to be provided in compact housings with space and cost requirements comparable to those of 180.degree. disc-type systems.
Accordingly, it is a general object of the present invention to provide a new and improved fault indicator.
It is a more specific object of the invention to provide a fault indicator having a more efficient and compact indicator flag assembly for indicating the occurrence of a fault current.
It is another object of the invention to provide a fault indicator having an improved 90.degree. segmental-type indicator flag assembly which is compact and economical to manufacture.